1. Field of the Invention
The present invention relates to a toroidal-type continuously variable transmission which is used, for example, as a transmission for a vehicle.
2. Description of the Related Art
A toroidal-type continuously variable transmission of a double cavity type used, for example, as a transmission for a vehicle is structured as shown in FIGS. 16 and 17.
As shown in FIG. 16, inside a casing 50, an input shaft (center shaft) 1 is rotatably supported and, on the outer periphery of the input shaft 1, two input disks 2, 2 and two output disks 3, 3 are mounted. Also, on the outer periphery of the middle portion of the input shaft 1, an output gear 4 is rotatably supported. In the central portion of the output gear 4, cylindrical-shaped flange portions 4a, 4a are formed; and, the output disks 3, 3 are connected by splint connection to the flange portions 4a, 4a respectively.
The input shaft 1 can be driven and rotated by a drive shaft 22 through a loading-cam-type pressing device 12 disposed between the input disk 2 situated on the left in FIG. 16 and a cam plate 7. Also, the output gear 4 is supported within the casing 50 through a partition wall 13 composed of two members connected together, whereby the output gear 4 can be rotated about the axis O of the input shaft 1 but is prevented from shifting in the direction of the axis O.
The output disks 3, 3 are supported by needle roller bearings 5, 5 each interposed between the input shaft 1 and themselves in such a manner that they can be rotated about the axis O of the input shaft 1.
Also, the input disk 2 situated on the left side in FIG. 16 is supported on the input shaft 1 through a ball spline 6, while the input disk 2 on the right side in FIG. 16 is spline connected to the input shaft 1; and, the two input disks 2 can be rotated together with the input shaft 1. And, between the inner surfaces 2a, 2a (concave-shaped surfaces) of the input disks 2, 2 and the inner surfaces 3a, 3a (concave-shaped surfaces) of the output disks 3, 3, power rollers 11 (see FIG. 17) are held in such a manner that they can be rotated.
In the inner peripheral surface 2c of the input disk 2 situated on the right side in FIG. 16, there is formed a stepped portion 2b; and, a stepped portion 1b formed in the outer peripheral surface 1a of the input shaft 1 is butted against the stepped portion 2b, while the back surface (in FIG. 16, the right surface) of the input disk 2 is butted against a loading nut 9. Due to this, the input disk 2 is substantially prevented from shifting in the axis O direction with respect to the input shaft 1. Also, between the cam plate 7 and the flange portion 1b of the input shaft 1, a countersunk spring 8 is interposed; and, the countersunk spring 8 applies a pressing force to the respective contact portions between the concave-shaped surfaces 2a, 2a, 3a, 3a of each disks 2, 2, 3, 3 and the peripheral surfaces 11a, 11a of the power rollers 11, 11.
Now, FIG. 17 is a section view taken along the line A-A shown in FIG. 16. As shown in FIG. 17, inside the casing 50, there are disposed a pair of trunnions 15, 15 each of which can be swung about a pair of pivot shafts 14, 14 disposed at positions twisted with respect to the input shaft 1. By the way, in FIG. 17, illustration of the input shaft 1 is omitted.
The two trunnions 15, 15 respectively include, in their respective two end portions which are situated in the longitudinal-direction (in FIG. 17, vertical-direction) of a support plate portion 16, a pair of bent wall portions 20, 20 which are formed to be bent on the inner surface side of the support plate portion 16. And, these bent wall portions 20, 20 form recess-shaped pocket portions P respectively for storing their associated power rollers 11 therein. Also, on the outer surfaces of the bent wall portions 20, 20, the pivot shafts 14, 14 are disposed in such a manner that they are concentric with each other.
A circular hole 21 is formed in the central portion of each of the support plate portions 16 and the base end portion 23a of a displacement shaft 23 is supported in the circular hole 21. And, in case where the trunnions 15, 15 are respectively swung about their associated pivot shafts 14, 14, the inclination angles of the displacement shafts 23 supported on the central portions of the trunnions 15, 15 can be adjusted. Also, on the peripheries of the leading end portions 23b of the displacement shafts 23 projecting from the inner surfaces of the trunnions 15, 15, there are rotatably supported the power rollers 11; and, the power rollers 11, 11 are interposed between the input disks 2, 2 and output disks 3, 3. By the way, the base end portions 23a and leading end portions 23b of the respective displacement shafts 23, 23 are eccentric to each other.
Also, the pivot shafts 14, 14 of the trunnions 15, 15 are respectively supported in such a manner that they can be swung and shifted in the axial direction thereof (in FIG. 16, in the front and back direction; and, in FIG. 17, in the vertical direction) with respect to a pair of yokes 23A, 23B; and, the yokes 23A, 23B prevent the trunnions 15, 15 from moving in the horizontal direction thereof.
As shown in FIG. 18, each of the yokes 23A, 23B is formed into a rectangular shape by press working or forging a blank member made of metal such as steel. In the four corners of the respective yokes 23A, 23B, there are formed four circular-shaped support holes 18, while the pivot shafts 14 disposed on the two end portions of the trunnion 15 are swingably supported on the support holes 18 through radial needle roller bearings 30.
Also, in the width-direction (in FIGS. 17 and 18, the right-and-left direction) central portion of each of the yokes 23A, 23B, there are formed circular-shaped engaging holes 19, while the inner peripheral surfaces of the engaging holes 19 are formed as spherical-shaped concave surfaces; and, spherical-shaped surface posts 64, 68 are respectively fitted into the engaging holes 19. That is, the yoke 23A situated on the upper side is swingably supported by the spherical-shaped surface post 64 which is supported on the casing 50 through a fixing member 52, while the lower-side yoke 23B is swingably supported by the spherical-shaped surface post 68 and the upper valve body 61 of a cylinder 31 supporting the spherical-shaped surface post 68.
By the way, the displacement shafts 23, 23 disposed on the trunnions 15, 15 are disposed at positions which are opposite by 180° to each other with respect to the input shaft 1. Also, the direction, in which the leading end portions 23b of the respective displacement shafts 23, 23 are eccentric to the base end portions 23a thereof, is the same direction (in FIG. 17, the reversed upward and downward direction) to the rotation direction of the two kinds of disks 2, 2, 3, 3. Also, the eccentric direction is a direction which is substantially perpendicular to the mounting direction of the input shaft 1. Therefore, the power rollers 11, 11 are supported in such a manner that they can be shifted slightly in the longitudinal direction of the input shaft 1. As a result of this, due to elastic deformation of each components based on thrust load generated by the pressing device 12, even when the power rollers 11, 11 tend to shift in the axial direction of the input shaft 1, an unreasonable force can be prevented from being applied to the respective composing parts of the toroidal-type continuously variable transmission and thus the shifting movements of the power rollers 11, 11 can be absorbed.
Also, between the outer surface of the power roller 11 and the inner surface of the support plate portion 16 so the trunnion 15, there are interposed a thrust ball bearing 24 and a thrust needle roller bearing 25, in this order, starting from the outer surface of the power roller 11 which are both thrust rolling bearings. Of these bearings, each of the thrust ball bearings 24 is structured such that, while supporting a thrust-direction load applied to the power roller 11, it allows the power roller 11 to rotate. Each of the thrust ball bearings 24 comprises a plurality of balls 26, 26, a circular-ring-shaped retainer 27 for holding the balls 26, 26 in such a manner that the balls 26 are allowed to roll, and a circular-ring-shaped outer race 28. Also, the inner race raceway of each thrust ball bearing 24 is formed in the outer surface of the power roller 11, whereas the outer race raceway thereof is formed in the inner surface of the outer race 28.
Also, the thrust needle roller bearing 25 is held by and between the inner surface of the support plate portion 16 of the trunnion 15 and the outer surface of the outer race 28. And, the thrust needle roller bearing 25 is structured such that, while supporting a thrust load applied to the outer race 28 from the power roller 11, it allows the power roller 11 and outer race 28 to swing about the base end portion 23a of their associated displacement shaft 23.
Further, on the one-end portions (in FIG. 17, the lower end portions) of the trunnions 15, 15, there are disposed drive rods (trunnion shafts) 29, 29 and, on the outer peripheral surfaces of the middle portions of the drive rods 29, 29, there are fixedly mounted drive pistons (oil-pressure pistons) 33, 33. And, these drive pistons 33, 33 are respectively oil-tight fitted into the drive cylinder 31 composed of the upper and lower valve bodies 61, 62. The drive pistons 33, 33 and drive cylinder 31 cooperate together in constituting a drive device 32 which can shift the trunnions 15, 15 in the axial directions of the pivot shafts 14, 14 of the trunnions 15, 15.
In the case of the thus-structured toroidal-type continuously variable transmission, the rotational movement of the input shaft 1 is transmitted through the pressing device 12 to the respective input disks 2, 2. And, the rotational movements of the input disks 2, 2 are transmitted through the pair of power rollers 11, 11 to the output disks 3, 3 and further the rotational movements of the output disks 3, 3 are taken out from the output gear 4.
To change a rotation speed ratio between the input shaft 1 and output gear 4, the pair of drive pistons 33, 33 may be shifted in the mutually opposite directions. With the shifting movements of the drive pistons 33, 33, the pair of trunnions 15, 15 are shifted in the mutually opposite directions, For example, the power roller 11 on the left side in FIG. 17 is shifted downwardly, whereas the power roller 11 on the right side is shifted upwardly. This changes the directions of tangential-direction forces acting on the contact portions between the peripheral surfaces 11a, 11a of the power rollers 11, 11 and the inner surfaces 2a, 2a, 3a, 3a of the input and output disks 2, 2, 3, 3. And, due to such change in the directions of these forces, the trunnions 15, 15 are swung in the mutually opposite directions about the pivot shafts 14, 14 pivotally supported on the yokes 23A, 23B.
This changes the contact positions between the peripheral surfaces 11a, 11a of the power rollers 11, 11 and the inner surfaces 2a, 3a of the input and output disks 2, 3 to thereby change a rotation speed ratio between the input shaft 1 and output gear 4. Also, in case where a torque to be transmitted between the input shaft 1 and output gear 4 varies and the elastic deformation quantities of the respective composing parts vary, the power rollers 11, 11 and outer races 28, 28 belonging to these power rollers 11, 11 are slightly rotated about the base end portions 23a, 23a of the displacement shafts 23, 23. Since the thrust needle roller bearings 25, 25 are interposed between the outer surfaces of the outer races 28, 28 and the inner surfaces of the support plate portions 16 respectively constituting their associated trunnions 15, 15, the slight rotational movements of the power rollers 11 and outer races 28 can be carried out smoothly. Therefore, the force necessary to change the inclination angles of the displacement shafts 23, 23 in the above-mentioned manner can be reduced down to a small level.
By the way, the yokes 23A, 23B, which support the pivot shafts 14, 14 of the trunnions 15, 15 swingably and shiftably in the axial direction, are structured such that, as described above, they can be swung about the spherical-shaped surface posts 64, 68 (for example, see U.S. Pat. No. 6,117,043). However, conventionally, there has been desired the development of a structure that can swing the yokes 23A, 23B more smoothly.
In attaining this desire, in JP-A-9-291997, there is disclosed a technique which can swing the yokes 23A, 23B about pins inserted into pin holes formed in the yokes 23A, 23B.
However, in this technique, when forming the pin holes in the yokes 23A, 23B, the formation positions of the pin holes must be set with high accuracy. This not only makes it difficult to manufacture the yokes 23A, 23B but also makes it necessary to provide the pins specially, which results in the increased number of parts used in the toroidal-type continuously variable transmission and in the increased manufacturing cost thereof.